1. Technical Field
The present invention relates in general to packet switching network communications and, in particular, to frame relay networks. Still more particularly, the present invention relates to methods for establishing a virtual path capability in a frame relay network.
2. Description of the Related Art
Frame relay networks provide high speed virtual private network (VPN) capable of point-to-point high speed data transmission. Frame relay systems delimit and align frames on a channel using flags identifying the beginning and ending of a frame. Frame relay systems typically support virtual circuit multiplexing and demultiplexing through the use of a Data Link Connection Identifier (DLCI) in the frame. A DLCI identifies a virtual connection on a channel at a user to network or network to network interface. Consequently, A DLCI specifies a data link layer entity to which information is delivered or received from. A DCLI is specified in a particular field in each frame in the data link layer. The DLCI field may be either unstructured or structured.
FIG. 1 shows a diagram of a particular network for illustrating concepts of prior art as well as the present invention. A source user 10 sends a message over a prior art system to a destination user at address 64.2.3.4. A router 10 which receives the traffic to this destination, references an internal routing table, determines that this address is mapped with DLCI 27. Router 12 then puts the contents of the message in a frame and sets the DCLI field to DLCI 27 before sending this frame over the Frame Relay network. The frame is received by a first switching node which then consults its internal routing table to determine that the frame is to be mapped to DLCI 992. After performing the mapping, first switching node 16 relays the frame to a second switching node 18 which maps the frame to DLCI 35 and then sends the frame to router 20 which forwards the frame to the destination user at address 64.2.3.4.
As described above, DLCIs are pre-mapped to a particular destination. A routing table within each switching node specifies the proper output port for each DLCI frame. A unique DLCI is required to establish each of a plurality of virtual circuits which utilize a single switching node even though each of the plurality of virtual circuits connect to a single switching node over a common trunk. The DLCI field in each frame typically has only 10 bits and most of the possible bit combinations are reserved or used to convey specific user information. As a result there is a limited supply of unique DLCIs available. Furthermore, connectionless operations could be established within a network if the requirement is met that each frame arrives at the correct port designated by the destination identifier.